Just wanna share some thoughts I gained after many IT cases for years:
1. Get the info at the soonest by any chance if possible. Decision made in rush usually makes you regret.
2. Sometimes user are not aware what they've done which caused the problem (or they don't even know what happened). It is no harm to check with them for more info before troubleshoot, but try out your own for confirmation.
3. Learn not to be angry when someone spoke something you feel offended. They might not mean to challenge you, it could be just their normal habit. Take a deep breath and walk away if they can't take reason rationally (best if you equipped yourself with self defense skills :P ).
4. The more you learned, the more you know what you're lack of. Never feel embarrassed to ask others for info you really don't know. Keep your mouth shut & listen more when they explain. You may do further investigation later if you feel doubt (something similar in rule 2).
5. Say "sorry" if it really is your fault. You need courage to do so. Also you better have a remedy plan for the chaos you've caused.
6. Never ever attempt to think you can out smart others. You never know how many 'smart a**es' surrounding you. At the end you're the one who looks like a silly monkey at the public.